From WO 97/01168, a system is known for the digital processing of audio signals which is particularly suitable for disc jockeys and scratch artists. The speed and direction of a digital audio signal, for instance derived from a CD player, can be controlled according to this citation by the manual control of a rotational element. This rotational element is placed for instance on a turntable of a conventional record player and is being read by means of an optical sensor determining the speed and direction of rotation of the turntable. The data that are obtained thereby are being used to control the speed and direction of reproduction of the CD player. The problem associated with this known apparatus is, however, that is hardly usable by disc jockeys and in scratch applications for the reason that from a given position of the reading head of the CD player only continuously developing relative movements are possible that depend on the control of the earlier mentioned rotational element. In the known apparatus, it is for instance not possible to make swift reproductions of different musical segments on the CD in a way that is reproducible and can be controlled satisfactorily. Also the authentic scratch sound which can be realised by means of a conventional record, cannot be obtained with the known apparatus.